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2020 Mid-Atlantic Severe Weather - General Thread


Kmlwx
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  • 2 weeks later...
6 hours ago, Kmlwx said:

Destined to flip at some point. Likely just in time for spring. April is bound to be rainy and raw. 

Knowing our luck... probably.:lol:

My ideal pattern over the next couple months, say through June, would be for this pattern to last through early May. Then the NAO will tank to strongly negative from say May 10th onward while a ridge builds into western Canada over a trough in the western US (-EPO/-PNA) allowing for a ridge to build over the southern 1/2 to 2/3rds of the nation east of the Rockies while a trough gets locked in between the Great Lakes and Hudson Bay in response to the ridge nosing into western Canada(-EPO) AND the ridge over Greenland (-NAO). Think May 30-31, 1998 but through the Ohio Valley and Mid-Atlantic instead.

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38 minutes ago, George BM said:

Knowing our luck... probably.:lol:

My idea pattern over the next couple months, say through June, would be for this pattern to last through early May. Then the NAO will tank to strongly negative from say May 10th onward while a ridge builds into western Canada over a trough in the western US (-EPO/-PNA) allowing for a ridge to build over the southern 1/2 to 2/3rds of the nation east of the Rockies while a trough gets locked in between the Great Lakes and Hudson Bay in response to the ridge nosing into western Canada(-EPO) AND the ridge over Greenland (-NAO). Think May 30-31, 1998 but through the Ohio Valley and Mid-Atlantic instead.

@Eskimo Joe, @yoda, @high risk - @George BM is calling for SPC to issue a HIGH RISK for somewhere in the Mid-Atlantic or Northeast ;) 

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Maybe a slight chance for a MRGL late Wednesday?  From afternoon AFD from LWX:

Stronger low pressure will develop near the Appalachains Wednesday
as northern and southern stream energy phase in a deepening trough
over the central CONUS. The low will track through our area
Wednesday night as it strengthens and the cold front associated with
the low will also pass through during this time. More showers are
likely ahead of the low Wednesday into Wednesday night. A deeper
meridional flow ahead of this system and a strong temperature
difference between the airmass overhead and arctic air that will be
moving into the north-central CONUS means that the wind field will
be strong throughout all levels of the atmosphere. As the trough
axis swings toward a neutral and even negative tilt, this will cause
low pressure to strengthen nearby. A strong wind field aloft
suggests that showers could contain gusty to perhaps locally
damaging wind gusts late Wednesday into Wednesday night. Confidence
remains low at this time due to limited instability.

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8 hours ago, Kmlwx said:

The low pressure on the Euro doesn't pass as close to us as the event a few weeks ago. But the H5 chart is ripe looking. 

 

     Great looking 500 map for sure.     Right now, most of the guidance I've seen keeps the warm front south of the DC metro area, but it's obviously still 5 days out.....

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From this afternoon's AFD for Wed afternoon/evening:

Stronger low pressure and its associated cold front will
approach the area Wednesday afternoon before passing through
Wednesday evening. Showers are expected along and ahead of the
boundary during this time. The upper-level trough associated
with this system will swing negatively tilted while a potent
jetmax passes through the area. Strong directional convergence
along the cold front along with strengthening wind at all levels
of the atmosphere suggests that isolated thunderstorms with
gusty to perhaps damaging winds are possible. Shear profiles and
dynamic forcing are strong, but confidence for severe
thunderstorms remains low due to limited instability. With low
pressure passing directly overhead, an isolated spin up cannot
be ruled out either if instability can get rooted within the
boundary layer.

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So we're in to the range of the NAM nest now, and it has been emphatic for several consecutive cycles now that a strongly forced convective line will move through the area early Wednesday evening.      But it's also been emphatic that the line will not be surface-based, and most of the guidance I've seen agrees with that, so the chances of taking advantage of the excellent shear profiles seems low.     That said, the GFS is trying harder to find a tiny bit of sac-based instability, so I won't totally close the door, even though I'm really hesitant to consider the GFS it wants to scour out the low-level cold air.    

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10 hours ago, high risk said:

So we're in to the range of the NAM nest now, and it has been emphatic for several consecutive cycles now that a strongly forced convective line will move through the area early Wednesday evening.      But it's also been emphatic that the line will not be surface-based, and most of the guidance I've seen agrees with that, so the chances of taking advantage of the excellent shear profiles seems low.     That said, the GFS is trying harder to find a tiny bit of sac-based instability, so I won't totally close the door, even though I'm really hesitant to consider the GFS it wants to scour out the low-level cold air.    

Classic early season "high shear low CAPE environment"

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51 minutes ago, Eskimo Joe said:

Classic early season "high shear low CAPE environment"

         I'm always interested in high shear low CAPE setups, but it could be a high shear NO CAPE setup.        I tend to trust the NAM nest when it keeps us cool at the sfc in these events, but if the HRRR is right, it would be a SLGT risk day for sure.

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Just now, high risk said:

         I'm always interested in high shear low CAPE setups, but it could be a high shear NO CAPE setup.        I tend to trust the NAM nest when it keeps us cool at the sfc in these events, but if the HRRR is right, it would be a SLGT risk day for sure.

Yea, it's always a battle of the wedge.  I've noticed that when you get a maturing/mature storm with decent low level jet moving into us it's easier to clear out the low levels.  When you have to wait on the jet to strengthen over us then it's sketchy.  I would imagine it might not be as hard to scour out the low level cold air this time because we have no snow cover and the ground isn't frozen up.

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Late morning update from LWX:

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
Wednesday will start cloudy with areas of drizzle and fog. Ceilings should gradually lift through the day. A second area of low pressure will form along the Blue Ridge and develop
northeastward as it reaches southern New England by 12Z
Thursday. A deepening upper trough taking a negative tilt will
provide large scale forcing for upward vertical motion with
widespread showers and scattered thunderstorms expected Wed
afternoon through late evening. Given strengthening wind fields
aloft and increasing shear values, isolated severe thunderstorms
are possible late Wed into early evening before line of showers
and embedded t-storms reaches the Chesapeake Bay by 03Z Thu.
Cold air will filter in quickly on NW flow with snow showers
likely accumulating 1-3 inches over western Grant and Pendleton
Counties. Blustery on Thu with winds gusting up to 40 mph.
 

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LWX is pretty bullish in their afternoon AFD, and as Yoda mentioned, the MRGL risk now comes into the DC metro area.     I still, however, haven't seen guidance showing surface-based instability here.     I do see good mid-level lapse rates, so there will likely be some elevated cape, and I certainly believe that some lightning is possible.   Until, however, I see some sfc-based instability being progged, I can't buy in to SVR potential until you get well south of the DC Beltway.

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